DESCRIPTION: This application explores the discovery that a circadian clock found in photo receptors is regulated by a mechanism that includes a transcription/translation mechanism and provides output into a number of systems that show rhythmic behavior including transcription of some genes. To explore these observations, there are four specific aims: 1) to clone and characterize rhythmic mRNAs, 2) to analyze the regulation of rhythmic messenger RNAs by light and dopamine to explore their relationship to the clock, 3) to determine if the rhythmic gene products in Xenopus are rhythmically regulated in other vertebrate retinas or other circadian clock systems and 4) to develop a transfectable culture system suitable to study rhythmic gene expression in the retina.